The Role of Sunlight Exposure in Developing Cataracts Over Time

Overview 

Sunlight exposure, particularly ultraviolet (UV), has benefits and risks. Thanks to global sunscreen marketing, we are attuned to sun protection against skin cancer and photoaging. But many are still unaware that sunlight exposure can lead to visual impairments like cataracts.

A cataract is synonymous with a cloudy eye lens. This blinding eye disease can affect anyone but it predominates in older people.¹ With age, the proteins in the eye lens gradually break down and clump together, making the lens cloudy. UVA accelerates this process by penetrating our eye lens.²

Read on to understand how prolonged exposure to sunlight or UV radiation increases one’s chance of developing early cataracts and the preventive measures.

Sunlight and your eyes: Effects and risks

Sunlight includes ultraviolet (UV), visible (light), and infrared radiation (IR). UV radiation (UVR) is subdivided into UVA, UVB, and UVC. Midday, 95 % of the UV component of the sunlight is UVA, while 5 % is UVB. All of UVC and 90 % of UVB are absorbed by the earth’s atmosphere.³

A person’s exposure to UV depends on the following factors:³

• Season
• Time of the day
• Geographic latitude
• Altitude
• Clouds and haze
• Surface reflection
• Air pollution

UVR with energy higher than visible (light) or infrared radiation can cause biological damage.⁴ Among UVA and UVB, UVA penetrates deeper into the body. UVA is more likely to reach the eye lens.² Whereas UVB is absorbed greatly by the corneas.³

Figure 1. Cross-sectional view of a human eye. By Hariadhi. Wikimedia Commons [Internet]. Available from: Wikimedia Commons; [Public domain]

Overexposure of the eyes to sunlight (or UV) has been associated with eye cancers, keratopathy, pterygium, pinguecula, and early cataract.⁴

Understanding cataract through the lens of a normal eye

Ocular lens: What you need to know

The eye is an organ that focuses visible light through its lens, allowing us to see an object (Figure 2). The transparent lenses change their shape due to their distinct structure and protein composition, aiding in image formation.⁵ 

Figure 2. An eye lens focuses light on the retina by changing its shape, allowing the brain to perceive an object. By Tgru001. Wikimedia Commons [Internet]. Available from: Wikimedia Commons; [Public domain]

The function of the lens is achieved by its proteins (crystallins and albuminoids) and their unique packing (tightly packed). Crystallin proteins of the lens are of three types:⁵

• α-crystallins are structural proteins in the eye lens, with an additional role in maintaining the transparency of the lens by preventing aggregation or clumping of its proteins
• β-crystallins are structural proteins
• γ-crystallins are small-structural proteins in the lens

The crystallin proteins formed during embryonic development last a lifetime and are continuously maintained by the α-crystallins.^5,6 Any changes in the structural proteins could lead to protein clumping, compromising the lens transparency and function.⁵

α-crystallins and aging: The development of cataracts in the elderly

As we age, the α-crystallin proteins in the lens, which are as old as we are, undergo irreversible changes. These changes modify the original structure of α-crystallins, thereby affecting their ability to maintain other proteins.⁵

Other lens proteins, like β- and γ-crystallins, change structure when α-crystallins can no longer maintain them, leading to their breakdown.⁵

γ-crystallins, the smaller structural proteins, are more prone to clumping as the eye ages.^5,6 The clumped proteins accumulate in the eye lens, causing clouding that leads to cataracts.

Figure 3. An eye with a cataract. Unknown author. Wikimedia Commons [Internet]. Available from: Wikimedia Commons; [Public domain]

What happens if the clear eye lens turns opaque or cloudy?

A cloudy eye lens, or a cataract, obstructs the passage of light through the eye lens to the retina, thus affecting the vision.¹ As the cloudiness in the eye lens increases (cataracts gradually progress), vision deteriorates from blurry, hazy, and dull to its complete loss.

Learn more about the signs and symptoms of cataracts.

Sunlight exposure: The role of UV in accelerating the cataract process

UVA can reach the eye lens 1000 times more than UVB. UVR reportedly causes oxidative damage to the crystallin proteins in the eye lens.² 

Here, oxidative damage refers to the UVR effects causing harmful changes to the lens proteins (e.g., forming unwanted bonds in the protein resulting in clumping).⁵ These changes would otherwise occur only as the eye ages. Therefore, UVR promotes cataract formation.

UV radiation promotes cataract development: An elaboration

Our eye lenses have UV filters that absorb UVR. However, continued exposure of the UV filters to UVR in the sunlight, especially UVA, can form free radicals (natural by-products of biochemical reactions) or reactive oxygen species (unstable molecules with oxygen).^2,5

Free radicals, or reactive oxygen species (ROS), are bad news if they accumulate in the body after the body’s antioxidant mechanism fails. In a healthy system, the antioxidant defence mechanism neutralises the ROS and keeps their levels in check.

When this mechanism fails, the accumulating, highly unstable free radicals, or reactive oxygen species (ROS), can trigger unwanted chain reactions that eventually disrupt and damage the whole cell.

In the lens, the chain reaction triggered by free radicals or ROS produces more free radicals or ROS, amplifying undesired changes in α-crystalline structures. Therefore, leading to loss of α-crystallin function and clumping of lens proteins.^2,5 

The clumped proteins deposit in the eye lens, making them cloudy. Thus, UVR promotes early cataract development.

Ways to protect your eyes from sunlight and early cataracts

Protecting your eyes is the best way to delay cataracts. Wearing sunglasses and a hat is the simplest and most efficient way to protect your eyes from the sun’s UVR.

Sunglasses shield your eyes from harmful UV rays

Wearing sunglasses to protect your eyes makes you ‘cool.’ However, wearing it the right way is what protects them:⁷

• The effectiveness of a sunglass depends on its lenses’ transmittance (pass-through) and its geometry
• Low transmittance lenses are preferred because they allow less UVR to pass through
• Close-fitting goggles provide the best sun protection as they completely cover the eyes in all directions
• Middle-sized sunglasses provide better sun protection compared to large-sized sunglasses
• The fit of sunglasses matters, as loose-fitting sunglasses may fail to protect the eyes from reflected UVR (ground or overhead)

To give you context, wearing sunglasses with UVA/UVB protection (UV400 marking) that does not provide a tight fit to the head’s geometry will not offer the best sun protection because the sun's rays could bypass the sunglasses through the gaps.

Remember that ineffective, prolonged use of sunglasses while outdoors might increase UVR doses received due to pupil dilation.⁷

Understand how UV-blocking sunglasses work. Also, check the tips for choosing the best sunglasses. 

Don't forget your hat: Simple sun protection for your eyes

Wearing sunglasses with a hat or umbrella can improve eye protection by significantly reducing the UV dose reaching them.⁷ A hat with a broad, dark brim or a simple cap with a bill that shades your eyes and reduces glare are also good and convenient options.

A hat is a practical solution to protect your child’s vulnerable eyes from UVR. A sun safety and intervention program for outdoor workers, especially the farmers, found their preference for wide-brimmed hats as a convenient option to minimise the eyes’ sunlight exposure over sunglasses.⁸

Sun protection goes beyond summer

In summer, 75 % of the UVR is received between 9:00 AM and 3:00 PM, of which 20–30 % is received between 11:00 AM and 1:00 PM solar time (based on the sun's position).³ 

UV levels are highest around solar noon (4 hours) in summer due to the direct path of the sun's rays to Earth. It is best to avoid overexposure to sunlight during this time.

Also, the UVR varies with seasons (not much if you stay close to the equator), latitude (high UVR in regions closer to the equator), presence of clouds (lower UVR), and surface reflectance (fresh snow reflects 85–90 % of incident UVB). 

Hence, it is safe to protect your eyes from sunlight with the right pair of sunglasses and/or a hat, all seasons, year-long, without obsessing over the UV index for the day.

FAQ’s

Can dietary changes slow down the progression of cataracts?

Yes, dietary changes could delay cataract formation. Studies have indicated a positive relation between diet and cataract incidence.⁹

Vitamins, particularly vitamin C, E, B9, and β-carotene, were found to slow down or lower the formation of cataracts. Surprisingly, dietary intake of vitamins has more significant protective effects than supplements.⁹

Increased consumption of plant produce, including fruits and vegetables, in addition to skimmed yoghurt and fish, is beneficial in delaying the onset of age-related cataract.⁹ Explore the best foods with eye-healthy nutrients.

Also read how carrots, dragonfruits, oranges, and persimmons help in maintaining good eye health. 

The antioxidant properties of the nutrients prevent the oxidative damage induced by UVR in lens proteins.³

How often should I consult an ophthalmologist (eye doctor)?

The onset of cataracts is gradual and progressive. Though cataract cases are reported in children, it is a common old age-related eye disease, typically seen when one is in their 50s and 60s.¹

As it is gradual, early detection of the condition through routine eye examinations can help preserve vision. How often is the routine? If you fall within the age range, you can get your eyes examined once every 1 to 2 years.

However, if you have conditions like diabetes, myotonic dystrophy, atopic dermatitis, neurofibromatosis type 2, or hypothyrodism, consider getting annual eye check-ups.¹

Summary

• The eye lens that plays a specialised role in our sense of sight is transparent
• α-crystallin, a structural protein in the lens with an important chemical function, renders the lens its transparent and optical properties
• Overexposure to sunlight or its UV radiation can cause oxidative damage to α-crystallin
• Oxidative damage of α-crystallin results in its loss of function, causing lens proteins to clump
• When crystallin proteins clump, the eye lens is no longer transparent or develops a cataract
• The early onset of cataracts triggered by UV radiation can be avoided by protecting your eyes with sunglasses or a brimmed hat